Field of the Invention
The invention relates to a steam turbine component and a steam turbine with a throttle element which can be displaced essentially along a main axis, in particular the main axis of the turbine, for regulating steam flow through a flow passage provided in a separating element that is disposed in and fills a cross-sectional area extending at right angles to the main axis.
Various control elements are known for regulating the steam flow in a steam turbine. A comparison of control elements based on valves and on rotary valves is described in an article entitled "Der Drehschieber als Regelorgan fur Entnahme-Dampfturbinen The Rotary Valve as a Control Element for Extraction Steam Turbines! by K. Speicher and E. Mietsch, in the publication Maschinenbautechnik, Berlin, Volume 15, No. 4, 1966, pages 185 to 190. A further control element is known from German Published, Non-Prosecuted Patent Application DE 1 426 792.
Axial and radial flow valves are mentioned as possible forms of rotary valves. The valves are used to completely or partially shut off openings which are provided in a nozzle cover extending over the cross-section of the steam turbine. A first form of a valve includes a ring, which can be rotated in the circumferential direction, which has openings analogous to the openings in the nozzle cover and though which a flow occurs axially. The flow through the openings of the valve takes place in the axial direction, i.e. in the direction of the main axis of the steam turbine. In a second form, a rotatable ring is again provided but the flow through that ring takes place in the radial direction, for which purpose the openings in the nozzle cover cause a deflection of the flow from the radial to the axial direction. The valve is then in contact over a large area with a corresponding deflection part of the nozzle cover. Motion of the valve must therefore take place against a substantial frictional resistance. In a third configuration, radially displaceable annular segments are provided for closing the openings in the nozzle cover. A radial flow valve with an axially displaceable ring is described as a fourth configuration, with the nozzle cover in that case again having a flow-deflecting projecting structure on which the axially displaceable ring is guided. The problem of large frictional forces which have to be overcome also arises in that case. Although complete static balancing is possible during throttle control in the radial rotary valves mentioned above, a relatively large radial gap must be provided in order to ensure free thermal expansion. Due to that fact, it is not possible to close the nozzle cover opening completely and leakage losses due to an undesirable flow of steam must be accepted.
When the known axial rotary valves are employed, large contact and frictional forces occur which lead to corresponding wear of the parts that slide on one another. In addition, large actuation drives are to be provided for the operation of such axial rotary valves. Complicated and expensive structures with balancing surfaces are known for reducing the contact forces. However, they involve a corresponding space requirement in the radial direction. Those structures are therefore unusable in practice in the case of turbines of the reaction type. As a result of the known disadvantages, rotary valves are currently used at relatively low extraction steam pressures, if at all.